A virtual tape apparatus is an apparatus that virtually carries out tape operations by assigning a virtual tape volume to, and storing data in, storage apparatus whose access speed is faster than that of a tape library apparatus. This virtual tape volume is called a logical volume. As a storage apparatus that stores data, for example, a disc array apparatus and the like is used, and to the back end of the virtual tape apparatus, a tape library apparatus is connected in many cases.
When there is no empty space in the storage apparatus, one of the logical volumes is written into the magnetic tape in the tape library apparatus, and is deleted from the storage apparatus. Then, when an access to the deleted logical volume occurs, the data of the logical volume is copied from the tape library apparatus to the storage apparatus. The operation of coping data of the logical volume from the tape library apparatus to the storage apparatus is called recall in some cases.
Meanwhile, a backup method to utilize redundant data for data restoration in a backup system in which data recorded in a disk apparatus is saved in a backup apparatus is also known (see Patent Document 1, for example).
In this backup method, data to be the backup target is divided into divided data of a specified size, and redundant data for data restoration is created for divided data that is less by one in number than the number of a plurality of data recording units that record data. Then, the corresponding divided data and redundant data are recorded respectively in different data recording units.
When restoring data, the corresponding divided data and redundant data are read in from the respective data recording units. When divided data could not be read in a normal manner from one of the data recording units, in the corresponding divided data and redundant data, the divided data that could not be read is crated using divided data and redundant data that could be read in a normal manner. Then, the data before the division is restored using the divided data.    Patent Document 1: Japanese Laid-open Patent Publication No. 2003-150325